Method of p-type doping of cadmium telluride

ABSTRACT

A method of p-type doping cadmium telluride (CdTe) is disclosed. The method comprising the steps of, (a) providing a first component comprising cadmium telluride (CdTe) comprising an interfacial region, and (b) subjecting the CdTe to a functionalizing treatment to obtain p-type doped CdTe, said functionalizing treatment comprising a thermal treatment of at least a portion of the interfacial region in the presence of a first material comprising a p-type dopant, and of a second material comprising a halogen. A method of making a photovoltaic cell is also disclosed.

BACKGROUND

The invention relates generally to the area of photovoltaic (PV) cells.More specifically, the invention relates to methods of making PV cellshaving a photo-active layer that includes cadmium telluride (CdTe). Theinvention also relates to methods of p-type doping of CdTe.

The solar spectrum “sunlight” contains a distribution of intensity as afunction of frequency. It can be shown that the conversion efficiencyfor utilizing sunlight to obtain electricity via semiconductors isoptimized for semiconducting band-gaps in the range vicinity betweenabout 1.4 to about 1.5 electron volt (eV). The semiconducting band-gapof CdTe, is a good match for this requirement.

p-type CdTe is currently one of the common commercially used materialsused in PV cells wherein the photo-active material is CdTe. Quitegenerally, in the interest of brevity of the discussions herein, PVcells including p-type CdTe as the photo-active material may be referredto as “CdTe PV cells.” Similarly, PV installations including CdTe PVcells would be referred to as “CdTe PV installations.” Commercialfeasibility of large-scale PV installations including p-type CdTe PVcells has been demonstrated, and the cost of electricity obtained fromsuch large-scale p-type CdTe PV installations is approaching gridparity. Commercial feasibility of smaller scale, that is, area confined,installations remains a challenge within the art due to the relativelypoor overall efficiency of such smaller scale installations. Despitesignificant academic and industrial research and development effort, thebest reported conversion efficiency “e_(B)” of p-type CdTe PV cells hasbeen stagnant at about 16.5% for close to a decade. This best reportedconversion efficiency may be compared to the entitlement-efficiency ofCdTe PV cells for the solar energy spectrum, whichentitlement-efficiency is about 23%. The conversion efficiency numbersmay further be compared to the “module” efficiency of typical currentlyavailable commercial large-scale p-type CdTe PV installations, whichmodule efficiency is lower, and is about 11%.

Evidently, any improvement in p-type CdTe PV cell efficiency will resultin an improvement in overall efficiency of corresponding CdTe PVinstallations. Such improvement will enhance the competitiveness of theCdTe PV installations compared to traditional methods of generatingelectricity, such as from natural gas or coal. It is evident thatimprovement in overall efficiency will enable p-type CdTe PV celltechnology to successfully penetrate markets where small-scale areaconfined installations are required, such as markets for domestic PVinstallations.

Currently known methods for manufacturing p-type CdTe PV cells oncommercially viable soda-lime glass substrates necessarily requirerelatively low temperature processes (performed typically attemperatures ˜<600 degrees Celsius (° C.)). Such necessity for lowtemperature processes, is one of the reasons why it has not beenpossible to enhance p-type doping levels beyond a doping level “c_(M),”wherein c_(M)˜5×10¹⁴ per cubic centimeter (/cm³). The inability toachieve p-type doping levels within CdTe, that are substantially inexcess of c_(M), is among the factors resulting in the currentstagnation of the conversion efficiencies at about e_(B).

There is a need within the art for methods of fabrication via whichimproved p-type CdTe PV cells having conversion efficiencies in excessof e_(M) can be obtained. For any such methods to be commerciallyfeasibly, they should be compatible with existing p-type CdTe PV cellfabrication process requirements such as for instance, the necessaryrequirement that the fabrication be performed at the relatively lowtemperatures mentioned above.

Methods whereby enhanced p-type doping levels within the photo-activeCdTe material can be obtained, which methods are yet compatible withextant p-type CdTe PV cell fabrication processes, would therefore behighly desirable.

BRIEF DESCRIPTION

Embodiments of the invention are directed to a magnetizer capable ofmagnetizing permanent magnets disposed in-situ a mechanical member sucha rotor.

A method of making a photovoltaic (PV) cell, said method comprising thesteps of, (a) providing a first component comprising a cadmium telluride(CdTe) layer comprising an interfacial region, (b) subjecting the firstcomponent to a functionalizing treatment to obtain a first greencomponent, said functionalizing treatment comprising treating at least aportion of the interfacial region with a first material comprisingcopper and a second material comprising chlorine, (c) subjecting thefirst green component to a first annealing treatment to obtain a secondgreen component, (d) subjecting the second green component to aprocessing treatment, and (e) disposing a second component adjacent theCdTe layer to form the PV cell.

A method for making a photovoltaic cell, said method comprising thesteps of, (a) providing a first component comprising a cadmium telluride(CdTe) layer comprising an interfacial region; (b) subjecting the firstcomponent to a functionalizing treatment to obtain a first greencomponent, said functionalizing treatment comprising soaking at least aportion of the interfacial region in the presence of a first solutioncomprising copper, (c) subjecting the first green component to a firstannealing treatment in the presence of a second solution comprisingchlorine to obtain a second green component, (d) subjecting the secondgreen component to a processing treatment, and (e) disposing a secondcomponent adjacent the CdTe layer to form the photovoltaic cell.

These and other advantages and features will be more readily understoodfrom the following detailed description of preferred embodiments of theinvention that is provided in connection with the accompanying drawings.

DRAWINGS

FIG. 1 is a flow-chart illustration of a method of making a PV cell,according to one embodiment of the invention.

FIG. 2 is a flow-chart illustration of a method of making a PV cell,according to one embodiment of the invention.

FIG. 3 is a side-cross section view of a first component, according toone aspect of the invention.

FIG. 4 is a side cross-section view of a PV cell, according to oneaspect of the invention.

FIG. 5 is a bar-chart of surface photo-voltage values obtained on aseries of second components, according to one aspect of the invention.

FIG. 6 shows operational characteristics data of PV cells, according toone aspect of the invention.

FIG. 7 is a bar-chart that compares the efficiency of a PV modulecomprising PV cells made according embodiments of the method disclosedherein, according to one aspect of the invention.

FIG. 8 is a flow-chart illustration of a method of making a PV cell,according to one embodiment of the invention.

FIG. 9 is a flow-chart illustration of a method of p-type doping CdTe,according to one embodiment of the invention.

DETAILED DESCRIPTION

In the following description, whenever a particular aspect or feature ofan embodiment of the invention is said to comprise or consist of atleast one element of a group and combinations thereof, it is understoodthat the aspect or feature may comprise or consist of any of theelements of the group, either individually or in combination with any ofthe other elements of that group.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Moreover, the use of “top,” “bottom,” “above,” “below,” and variationsof these terms is made for convenience, but does not require anyparticular orientation of the components unless otherwise stated. Asused herein, the terms “disposed on” or “deposited over” or “disposedbetween” refers to both secured or disposed directly in contact with andindirectly by having intervening layers therebetween.

As used herein, the term “adjacent,” when used in context of discussionof different regions and/or parts of, for instance, a PV cell, may referto the situation where the regions and/or parts under discussion areimmediately next to each other, or it may also refer to a situationwherein intervening regions and/or parts are present between the regionsand/or parts under discussion.

As used herein, the term “green,” when used in the context of adiscussion of a physical entity, such as a component, conveys that theentity is as yet in an intermediate stage of its manufacture, that is,one or more of the steps of the method employed to make or obtain thecomponent, from the entity, have as yet not been initiated or completed.For example, a “green component” refers to a physical entity on whichone or more steps of the method of making the component, wherein theobtained component displays desired or improved levels of certainphysical properties, such as, energy conversion efficiency, have as yetnot been performed.

As used herein, the term “interfacial region” when used in context ofdiscussion of a physical entity refers to the region at, and in thevicinity of, any interface that the physical entity has with thesurrounding environment. It is to be understood that the interfacialregion is “exposed,” in that, any entities present within theenvironment, such as chemical agents present within the environment,have direct physical access to the interfacial region.

As used herein, the term “functionalizing treatment” when used in thecontext of discussion of a physical entity such as a component or agreen component, refers to a treatment, including a chemical treatmentand/or a physical treatment of the physical entity, which treatmentresults in a substantial change in one or more physical properties, suchas dopant concentration, or energy conversion efficiency, of thephysical entity. The functionalizing treatment, may for instance, beperformed as part of a step of a method of making the component.

As discussed in detail below, embodiments of the invention are directedto improved methods of making a photovoltaic (PV) cell wherein thephotoactive layer includes p-type cadmium telluride (CdTe). Thephotoactive layer is the part of the PV cell where the electromagneticenergy of incident light occurs, for instance sunlight, is converted toelectrical energy (that is, to electrical current). Quite generally, inthe discussions herein it will be understood that, the term “p-type CdTePV cell,” or simply “CdTe PV cell” or “PV cell,” will refer to a PV cellwherein the photoactive layer includes p-type CdTe. Embodiments of theinvention disclosed herein provide also for improved methods of p-typedoping of CdTe.

An issue of significance in the context of current generation p-typeCdTe PV cells, is that, despite several years of research anddevelopment work by the industry and academia, it has not been possibleto enhance p-type doping levels within the CdTe layer beyond about c_(M)˜5×10¹⁴ /cm³. This is among the reasons that have limited thebest-reported efficiencies for p-type CdTe PV cells to about e_(B)˜16.5%.

The relatively low temperature processing conditions (typically ˜<500degrees Celsius (° C.)) needed for the fabrication of p-type CdTe PVcells is among the reasons why it has not been possible to enhancep-type doping levels within CdTe. This in turn has hampered thedevelopment of p-type CdTe PV cells with efficiencies approaching theentitlement-efficiency (˜23%) of CdTe PV cells for the solar energyspectrum. Quite generally, embodiments of the invention proposed hereinalso include methods of p-type doping CdTe, whereby p-type doping levelsare enhanced.

As discussed in detail below at least in relation to FIGS. 1-2, and FIG.8, embodiments of the invention disclosed herein provide methods formaking improved PV cells. FIGS. 5-7 show representative data ofoperational parameters obtained on p-type PV cells fabricated accordingto the embodiments of the presently disclosed methods. Furthermore, asdiscussed in detail in relation to FIG. 9, embodiments of the inventiondisclosed herein provide methods for achieving p-type doping levelswithin CdTe, enhanced over currently demonstrated p-type doping levelswithin CdTe.

FIG. 1 is a flow-chart illustration of a method 100 of making a PV cell,according to one embodiment of the invention. The method 100 includes astep 102 of providing a first component including a CdTe layer includingan interfacial region. This is to be followed by a step 104 ofsubjecting the first component to a functionalizing treatment to obtaina first green component, wherein the functionalizing treatment comprisestreating at least a portion of the interfacial region with a firstmaterial comprising copper and a second material comprising chlorine.This is to be followed by a step 106 of subjecting the first greencomponent to a first annealing treatment to obtain a second greencomponent. This is to be followed by a step 108 of subjecting the secondgreen component to a processing treatment (discussed below). This is tofollowed by a step 110 of disposing a second component adjacent the CdTelayer to form the PV cell. Fabrication protocols via which one mayobtain first component embodiments compatible for use during method 100would be known to one of skill in the art. A non-limiting fabricationprotocol is discussed further below.

In one embodiment of the invention, the first component provided in step102 includes a layer including at least one transparent conductingoxide. Non-limiting examples of suitable transparent conducting oxidesinclude, aluminum doped zinc oxide, indium tin oxide, fluorine tinoxide, cadmium tin oxide, or combinations thereof. In one embodiment ofthe invention, the first component provided in step 102 includes a layerincluding at least one high resistance oxide. Non-limiting examples ofsuitable high resistance oxides include, zinc tin oxide, aluminum oxide,tin oxide, gallium oxide, silicon oxide, indium oxide, or combinationsthereof. In one embodiment of the invention, the first componentprovided in step 102 includes a layer including cadmium sulphide.

In particular embodiments of the invention, the second material providedin step 104 includes cadmium chloride. Based on experiments, somerepresentative results of which experiments are presented in FIGS. 4-7,in one embodiment of the invention, a ratio of an amount of the firstmaterial to an amount of the second material, which first material andsecond material are as recited in step 104, lies within the range fromabout 0.01 parts per million (ppm) to about 100 ppm. In anotherembodiment of the invention, a ratio of an amount of the first materialto an amount of the second material, which first material and secondmaterial are as recited in step 104, lies within the range from about0.1 ppm to about 20 ppm. In yet another embodiment of the invention, aratio of an amount of the first material to an amount of the secondmaterial, which first material and second material are as recited instep 104, lies within the range from about 0.5 ppm to about 5 ppm.

In one embodiment of the invention, the first annealing treatment asrecited in step 106 is performed at temperatures that lie within a rangefrom about 300 degrees Celsius (° C.) to about 500° C. In anotherembodiment of the invention, the first annealing treatment recited instep 106 is performed at temperatures that lie within a range from about350° C. to about 450° C. In yet another embodiment of the invention, thefirst annealing treatment recited in step 106 is performed attemperatures that lie within a range from about 375° C. to about 425° C.In one embodiment of the invention, the first annealing treatmentrecited in step 106 is performed for a time period that lies within arange from about 1 minute to about 60 minutes. In another embodiment ofthe invention, the first annealing treatment recited in step 106 isperformed for a time period that lies within a range from about 5minutes to about 40 minutes. In another embodiment of the invention, thefirst annealing treatment recited in step 106 is performed for a timeperiod that lies within a range from about 10 minutes to about 20minutes. In particular embodiments of the invention, the first annealingtreatment recited in step 106 is performed so that an environment of thefirst green component during the first annealing treatment comprises anoxidizing environment. Non-limiting examples of oxidizing environmentsinclude air. It is likely that at a least a portion of the CdTe layer,as provided during step 102, is rendered substantially p-type after theperformance of step 106.

In particular embodiments of the invention, the processing treatmentperformed during step 108 includes a soaking treatment. In moreparticular embodiments of the invention, the soaking treatment includesthe use of a solvent including ethylene di-amine (EDA). In particularembodiments of the invention, the processing treatment performed duringstep 108 includes deposition of a copper layer on at least a portion ofthe interfacial region. In particular embodiments of the invention, theprocessing treatment performed during step 108 includes a secondannealing treatment.

In particular embodiments of the invention, the second componentprovided in step 110 includes a back-contact layer. In more particularembodiments of the invention, the back-contact layer includes aplurality of layers. In such specific embodiments of the inventionwherein the back-contact layer includes a plurality of layers, theback-contact may be assembled or disposed layer-by-layer, (that is, eachlayer of the plurality of layers is disposed sequentially), adjacent theCdTe layer. A non-limiting example of such layer-by-layer, or sequentialassembly of the back-contact layer includes a procedure whereby each ofthe plurality of layers is disposed one after another adjacent the CdTelayer. Non-limiting examples of methods via which the second componentmay be assembled or disposed adjacent the CdTe layer include depositionmethods including at least one of screen printing, sputtering,evaporating, electroplating, electrodepositing, or electroless plating.

As discussed, embodiments of the invention include a back-contact layercomprising a plurality of layers. In one non-limiting embodiment, theback-contact comprises three layers, wherein, the first of the threelayers comprises graphite deposited via a method comprising at least oneof screen printing; the second of the three layers comprises a metaldeposited via a method comprising at least one of sputtering,evaporating, electroplating, or electroless plating; and the third ofthe three layers comprises an electrode layer comprising a metalcomprising at least one of aluminum, nickel, palladium, titanium,molybdenum, chromium, or gold, and is deposited via a method comprisingat least one of sputtering, evaporating, electroplating, or electrolessplating. In another non-limiting embodiment, the back-contact comprisestwo layers, wherein, the first of the two layers comprises at least oneof zinc tellurium (for example, ZnTe), antimony tellurium (for example,Sb₂Te₃), arsenic tellurium (for example, As₂Te₃), tellurium (Te), orcopper tellurium (for example, Cu_(x)Te, wherein ‘x’ lies between oneand two) deposited via a method comprising at least one of sputtering,evaporating, electrodeposition, or electroless plating; and the secondof the two layers comprises a metal comprising at least one of aluminum,nickel, palladium, titanium, molybdenum, chromium, or gold, and isdeposited via a method comprising at least one of sputtering,evaporating, electroplating, or electroless plating. In yet anothernon-limiting embodiment, the back-contact comprises a single layer,wherein the single layer comprises a metal comprising at least one ofaluminum, nickel, palladium, titanium, molybdenum, chromium, or gold,and is deposited via a method comprising at least one of sputtering,evaporating, electroplating, or electroless plating.

FIG. 2 is a flow-chart illustration of a method 200 of making a PV cell,according to one embodiment of the invention. The method 200 includes astep 202 of providing a first component comprising a CdTe layercomprising an interfacial region. This is to be followed by a step 204of subjecting the first component to a functionalizing treatment toobtain a first green component, the functionalizing treatment comprisingsoaking at least a portion of the interfacial region in the presence ofa first solution comprising copper. This is to be followed by a step 206of subjecting the first green component to a first annealing treatmentin the presence of a second solution comprising chlorine to obtain asecond green component. This is to be followed by a step 208 ofsubjecting the second green component to a processing treatment. This isto be followed by a step 210 of disposing a second component adjacentthe CdTe layer to form the PV cell.

In one embodiment of the invention, the first component provided in step202 includes a layer comprising at least one transparent conductingoxide. Non-limiting examples of suitable transparent conducting oxidesinclude, aluminum doped zinc oxide, indium tin oxide, fluorine tinoxide, cadmium tin oxide, or combinations thereof. In one embodiment ofthe invention, the first component provided in step 202 comprises alayer including at least one high resistance oxide. Non-limitingexamples of suitable high resistance oxides include, zinc tin oxide,aluminum oxide, tin oxide, gallium oxide, silicon oxide, indium oxide,or combinations thereof. In one embodiment of the invention, the firstcomponent provided in step 202 comprises a layer including cadmiumsulphide.

In particular embodiments of the invention, the first solution recitedin step 204 includes a solvent. A non-limiting example of a suitablesolvent includes EDA. In more particular embodiments of the invention, aconcentration of copper within the first solution, as recited in step204, should lie within the range from about 0.01 ppm to about 100 ppm.

In particular embodiments of the invention, the first annealingtreatment recited in step 206 is performed at temperatures that liewithin a range from about 300° C. to about 500° C. In particularembodiments of the invention, the first annealing treatment recited instep 206 is performed for a time period that lies within a range fromabout 1 minute to about 60 minutes. In particular embodiments of theinvention, the first annealing treatment recited in step 206 isperformed so that an environment of the first green component during thefirst annealing treatment comprises an oxidizing environment. It islikely that the CdTe layer provided during step 202 is renderedsubstantially p-type after performance of step 206.

In particular embodiments of the invention, the processing treatmentperformed during step 208 includes a soaking treatment. In moreparticular embodiments of the invention, the soaking treatment includesthe use of an solvent including EDA. In particular embodiments of theinvention, the processing treatment performed during step 208 includesdeposition of a copper layer on at least a portion of the interfacialregion. In particular embodiments of the invention, the processingtreatment performed during step 208 includes a second annealingtreatment.

In particular embodiments of the invention, the second componentprovided in step 210 includes a back-contact layer. In more particularembodiments of the invention, the back-contact layer includes aplurality of layers. In such specific embodiments of the inventionwherein the back-contact layer includes a plurality of layers, theback-contact may be assembled step-by-step, or sequentially, adjacentthe CdTe layer. A non-limiting example of such step-by-step, orsequential, assembly of the back-contact layer includes a procedurewhereby each of the plurality of layers is disposed one after another,adjacent the CdTe layer. Non-limiting examples of methods via which thesecond component may be disposed adjacent the CdTe layer includedeposition methods including at least one of screen printing,sputtering, evaporating, electroplating, electrodepositing, orelectroless plating.

Considering for instance method 100, and not to be limited to anyparticular explanation or theory, it is likely that the chlorine asrecited in step 104 of method 100, acts as a fluxing agent, whereby thechlorine helps in reducing a temperature that is required forrecrystalization and grain growth, of the CdTe provided as part of thefirst component during step 102, during the first annealing treatment asrecited in step 106, which recrystalization and grain growth likelyresult in an enhancement of the electronic properties of the CdTe.

A representative non-limiting fabrication protocol via which one mayobtain first component embodiments compatible for use during methods 100or 200 is now discussed. A “batch” of first components is typicallyobtained or “cut” from the same sheet. A representative non-limitingfabrication protocol via which a sheet may be fabricated is nowpresented: a commercially available substrate comprising soda lime glassand having a layer comprising fluorine doped tin oxide deposited on itssurface was provided. On the layer comprising fluorine doped tin oxidewas deposited a layer comprising a high resistance oxide comprising zinctin oxide approximately 1000 angstroms (Å) in thickness via reactivesputtering using direct current in an oxygen ambient having pressurebetween about 1 milli Ton (mT) to about 5 mT. The target used for thedeposition of the layer comprising zinc tin oxide had a composition ofapproximately 5% zinc by weight and approximately 95% tin by weight. Onthe layer comprising zinc tin oxide was further deposited a layercomprising cadmium sulphide (CdS) approximately 1000 Å in thickness viaradio frequency (RF) sputtering in an argon ambient having pressurebetween about 5 mT to about 15 mT. On the layer comprising CdS wasdeposited a layer comprising cadmium telluride (CdTe) approximately 3micrometers in thickness via a modified close-spaced sublimation (CSS)method wherein the substrate temperature was maintained between about400° C. to about 600° C. It is mentioned that the CSS method used hereindiffers from more standard CSS methods known within the art in at leastone respect, whereby a distance between the location where the material(in the present instance, CdTe) is to be deposited and the source of thematerial is on the order of tens of centimeters, whereas in morestandard CSS methods, this distance is on the order of millimeters. Itis remarked that alternate protocols, for instance, protocols in whichdeposition of the layer comprising a high resistance oxide is omitted,may also be used to obtain sheets that are compatible for use withinembodiments of the present invention. It is remarked that, firstcomponents fabricated via other known fabrication methods are alsocompatible for use within embodiments of the invention disclosed herein.

Again, considering for instance, the method 100: not to be limited toany particular explanation or theory, when the first component providedduring step 102 comprises a layer comprising cadmium sulphide (CdS),then it is likely that the chlorine as recited in step 104 of method100, helps in an intermixing of the CdTe (also provided during step 102)and the CdS, so that a layer comprising CdS_(x)Te_(1-x) (where, ‘x’ liesbetween zero and one) is formed along the interface region between theCdTe and the CdS. Not to be limited to any particular explanation ortheory, it is likely that the presence of the layer comprisingCdS_(x)Te_(1-x) enhances the minority carrier lifetime in the CdTe.Furthermore, it is also likely that the chlorine acts as a p-type dopantwithin the CdTe. It is also likely that the chlorine getters defects tothe grain boundaries within the CdTe layer. Evidently, these discussionsremain substantially applicable for other embodiments of the inventiondisclosed herein, in particular, these discussions are applicable formethod 200.

FIG. 3 is a side-cross section view of a first component 300 as recitedwithin the methods 100, 200. The first component 300 includes a CdTelayer 302 comprising an interfacial region 304. As discussed herein, thefirst component may further include additional layers. For instance, thefirst component 300 includes four additional layers 306, 308, 310, 313,wherein the layer 306 comprises CdS, the layer 308 comprises at leastone high resistance oxide, the layer 310 comprises at least onetransparent conducting oxide, and layer 313 comprises a transparentsubstrate comprising glass. Surface 315 of the layer 313 may beconfigured to receive a light energy flux (not shown; see FIG. 4,reference numeral 417). These aspects of the invention will be discussedin more detail in context at least of FIG. 4.

FIG. 4 is a side cross-section view of a PV cell 400 made according toembodiments of the methods recited herein, for instance, methods 100,200. The PV cell 400 includes a first component 402 (similar to firstcomponent 300) including a CdTe layer 404. The first component 402further includes additional layers 406, 408, and 410, wherein layer 406comprises CdS, layer 408 comprises at least one high resistance oxide,and layer 410 comprising at least one transparent conducting oxide, and413 comprises a transparent substrate, for example glass. The PV cell400 further includes a second component 412. It is clarified that, eventhough the second component 412 shown in FIG. 4 includes only a singlelayer, second components including multiple layers fall within thepurview of the present invention. For instance, the second component 412may comprise a back-contact layer, wherein the back-contact layercomprises a plurality of layers. Based on the discussions herein, thoseof skill in the art may now appreciate that, before the second component412 is disposed adjacent to the CdTe layer 404 (for instance, as permethods 100, 200) to realize the PV cell as shown in FIG. 4, theinterfacial region (akin to interfacial region 308; see FIG. 3) of thefirst component 402 is subjected to treatments as recited in, forinstance, steps 104, 106, and 108, or as recited, for instance, in steps204, 206, 208. Surface 415 of the layer 413 may be configured to receivea light energy flux 417, at least a portion of which light energy flux417, when it continues on to the layer 404, results in thephoto-generation of charge carriers (electrons and holes), that is,results in the photovoltaic action of the PV cell 400.

FIGS. 5-6 show that the operational characteristics, such as surfacephoto-voltage (SPV) (FIG. 5), or current-voltage characteristics (FIG.6) of PV cells obtained via methods 100, 200, and equivalent andgeneralized methods thereof (discussed in relation to FIGS. 8-9), areenhanced over the operational characteristics of PV cells obtained viaconventional fabrication methods known within the art. FIG. 6 comparesthe energy conversion efficiency of module incorporating PV cellsobtained via methods 100, 200, to the energy conversion efficiency ofmodules incorporating PV cells obtained conventional methods known inthe art.

FIG. 5 is a bar-chart 500 of SPV values plotted along the ordinate 510for a series of “second” components, each of which series of firstcomponents were subjected to an illumination of about one Sun, or about100 milli watts per square centimeter. Each of the first components wassubstantially similar since they were obtained or “cut” from the samesheet which sheet was obtained as per the discussions presented earlier.

Consider for instance, bars 502 and 504. Bar 502 represents SPV valuedata obtained on a first component that was subjected to a soakingtreatment using EDA solution. No subsequent exposure to copper wasprovided. The resulting obtained component was then subjected to atreatment with cadmium chloride. The treatment with cadmium chloride wasperformed for about 20 minutes at a temperature of about 400° C. The SPVvalue represented by bar 502 was obtained on the thus obtained secondcomponent after the treatment with cadmium chloride. Consider now, thebar 504, which represents SPV value data obtained on a first componentthat was neither subjected to any soaking treatment, nor to anytreatment with a solution containing chlorine, as was the case for thefirst component corresponding to bar 502. It is clear that the SPVvalues represented by both bars 502 and 504, respectively at about 689milli volts, and about 690 milli volts, are substantially the same. Inother words, it is reasonably established that the SPV values aresubstantially unaffected by any soaking treatment.

Consider now the bars 506 and 508. Bar 506 represents SPV value dataobtained on a first green component that was obtained from a firstcomponent that was subjected to treatments as recited in steps 104 and106 of method 100. For instance, as part of performance of step 104, thefirst component was subjected to a functionalizing treatment to obtain afirst green component, the functionalizing treatment comprising treatingat least a portion of the interfacial region with a first materialcomprising copper and a second material comprising cadmium chloride. Aspart of performance of step 106, the first green component was furthersubjected to a first annealing treatment in air for about 20 minutes ata temperature of about 400 degrees Celsius to obtain a second greencomponent. Bar 508 represents SPV value data obtained on a first greencomponent that was obtained from a first component that was subjected totreatments as recited in steps 204 of method 200. For instance, as partof performance of step 204, the first component was subjected to afunctionalizing treatment to obtain a first green component, thefunctionalizing treatment comprising soaking at least a portion of theinterfacial region in the presence of a first solution comprising EDAand copper. As part of performance of step 206, the first greencomponent was further subjected to a first annealing treatment in airfor about 20 minutes at a temperature of about 400° C. to obtain asecond green component. The SPV values represented by both bars 506 and508, respectively at about 775 milli volts, and at about 797 volts, aresubstantially higher than the baseline SPV values represented by bars502 or 504, respectively.

It is evident from a comparison of bars 502, 504, with bar 506, or withbar 508, that the presence of the copper during the performance of thefunctionalizing treatment significantly enhances the SPV valueobtainable from the resulting second green component. Those of skill inthe art would appreciate that this enhancement in SPV value will likelyresult in an enhancement of the efficiency of a PV cell that includessuch a second green component.

FIG. 6 shows data that compares the effect on operationalcharacteristics (for instance, current-voltage “J-V” characteristics),due the use of different amounts of copper during performance of step104. FIG. 6 show current voltage “J-V” data sets 602, 604, and 606obtained on three PV cells that were made via embodiments of the method100, wherein differing amounts of copper were was used during theperformance of step 104.

The PV cells of FIG. 6 included first components that were obtained froma sheet that was substantially similarly prepared as the sheet fromwhich the first components were obtained in the example of FIG. 5.Accordingly, three first components was subjected to treatmentsaccording to method 100 wherein, a concentration of copper within afirst material (during performance of an embodiment of step 104) wasabout 0 parts per million (ppm) (FIG. 6, data represented via referencenumeral 602), that is, no copper was added to the first solution, about1.5 ppm (FIG. 6, data represented via reference numeral 604), and about4.5 ppm (FIG. 6, data represented via reference numeral 606)respectively, to obtain respective first green components. Following theperformance of step 104, in accordance with an embodiment of step 106,the obtained respective first green components were subjected to firstannealing treatment at about 400° C. for about 20 minutes in thepresence of a cadmium chloride solution to obtain respective secondgreen components. Following said performance of an embodiment of step106, in accordance with an embodiment of step 108, the respective secondgreen components were subjected to a processing treatment wherein acopper layer is deposited on the interfacial region. The processingtreatment further comprised a second annealing treatment, of the secondgreen component with the copper layer deposited on the interfacialregion, at a temperature of about 170° C. for about 12 minutes.Following said performance of an embodiment of step 108, in accordancewith an embodiment of step 110, a back-contact layer comprising graphitewas deposited adjacent the CdTe layer. The back-contact layer includedelectrodes comprising nickel and aluminum. Standard laser scribingprocesses were used to fashion said electrodes.

FIG. 6 shows J-V data-sets with the current “J” obtained being plottedalong the ordinate 608 as a function of the voltage “V” along abscissa610, for a given PV cell. For the particular data-sets shown in FIG. 6,the corresponding PV cells were illuminated over an aperture area ofabout 125 square centimeters, and with an illumination intensity ofabout one Sun. Beyond a voltage value of about 0.8 volts, it is evidentfrom FIG. 6 that the amount of current obtainable for a given voltagefor the PV cell corresponding to the data-set 604 is enhanced relativeto the PV cell corresponding to the data-set 602. Similarly, beyond avoltage value of about 0.8 volts, it is evident that the amount ofcurrent obtainable for a given voltage for the PV cell corresponding tothe data-set 606 is enhanced relative to the PV cell corresponding tothe data-set 604. In other words, as evidenced by the trend in the J-Vcharacteristics shown in FIG. 6, the operational characteristics of PVcells are a function of the amount of copper used during performance ofstep 104.

FIG. 7 is a bar-chart that compares the efficiency of a PV modulecomprising PV cells made according to an embodiment of the method 200,to the efficiency of a PV module comprising PV cells similarly made,without undergoing the functionalizing treatment of method 200. Each ofthe PV modules corresponding to the bars 702 and 704 had a total area ofabout 7200 square centimeters. It is evident that the performance of thefunctionalizing treatment to the PV cells results in an enhancement ofthe efficiency from a value of about 4.8% to about 8%. Since there is awell-known direct positive correlation between the current obtainablefor a given voltage from a particular PV cell, and the efficiency of thesame PV cell, a gestalt assessment of the data presented in FIGS. 6-7,would make evident to one of skill in the art, that the functionalizingtreatment in the presence of copper during the fabrication of PV cellsaccording the embodiments of the presently invented method, forinstance, method 200, results in PV cells with enhanced efficiency.

Based at least on the methods presented in FIGS. 1-2, and theexperimental results presented in FIGS. 5-7, it may now be evident thatthe presence of a p-type dopant (such as copper) during an annealingtreatment (for instance, the first annealing treatment as recited instep 106, or in step 206) substantially results in enhanced p-typedoping levels within a CdTe layer (for instance, the CdTe layer recitedin step 102, or in step 202), which enhancement in turn enables therealization of p-type CdTe PV cells having efficiencies enhanced overthe efficiencies of currently available p-type CdTe PV cells.Non-limiting examples of p-type dopants suitable for use withinembodiments of the present invention include copper phosphorus, arsenic,antimony, gold, silver, and bismuth. Non-limiting examples of halogenssuitable for use within embodiments of the present invention includechlorine.

FIG. 8 is a flow-chart illustration of another method 800 of making a PVcell, according to one embodiment of the invention. The method 800includes a step 802 of providing a first component comprising a CdTelayer comprising an interfacial region. This is to be followed by a step804 of subjecting the CdTe layer to a functionalizing treatment toobtain a green component, the functionalizing treatment comprising athermal treatment of at least a portion of the interfacial region in thepresence of a first material comprising a p-type dopant, and of a secondmaterial comprising a halogen, wherein the functionalizing treatmenteffects an incorporation of the p-type dopant into at least a portion ofthe CdTe layer. In other words, it is likely that the CdTe layerprovided during step 802 is rendered substantially p-type afterperformance of step 804. This is to be followed by step 806 ofsubjecting the green component to a processing treatment. This is to befollowed by step 808 of disposing a second component adjacent the CdTelayer to form the PV cell.

In one embodiment of the invention, the first component provided in step802 includes a layer including at least one transparent conductingoxide. Non-limiting examples of suitable transparent conducting oxidesinclude, aluminum doped zinc oxide, indium tin oxide, fluorine tinoxide, cadmium tin oxide, or combinations thereof. In one embodiment ofthe invention, the first component provided in step 802 includes a layerincluding at least one high resistance oxide. Non-limiting examples ofsuitable high resistance oxides include, zinc tin oxide, aluminum oxide,tin oxide, gallium oxide, silicon oxide, indium oxide, or combinationsthereof. In one embodiment of the invention, the first componentprovided in step 802 includes a layer including cadmium sulphide. It ismentioned that the methods via which one may obtain first componentembodiments compatible for use during method 100 or method 200(discussed earlier) are also substantially applicable to obtain firstcomponent embodiments compatible for use with method 800, or with method900 (discussed below).

In particular embodiments of the invention, the second material providedin step 804 includes cadmium chloride, hydrochloric acid, chlorine gas,or combinations thereof. Based on experiments, representative results ofwhich experiments are presented in FIGS. 5-7, in more particularembodiments of the invention, a ratio of an amount of the first materialto an amount of the second material, as recited during step 804, lieswithin the range from about 0.01 ppm to about 100 ppm.

In particular embodiments of the invention the thermal treatment recitedin step 804 includes a first annealing treatment. In particularembodiments of the invention, said first annealing treatment isperformed at temperatures that lie within a range from about 1 minute toabout 60 minutes. In particular embodiments of the invention, said firstannealing treatment recited is performed so that an environment of thegreen component during the first annealing treatment comprises anoxidizing environment.

In particular embodiments of the invention, the processing treatmentperformed during step 806 includes a soaking treatment. In moreparticular embodiments of the invention, the soaking treatment includesthe use of a solvent including at least one of EDA, a dilute solution ofbromine in methanol, or a mixture of nitric acid and phosphoric acid. Inparticular embodiments of the invention, the processing treatmentperformed during step 806 includes deposition of a copper layer on atleast a portion of the interfacial region (for instance, interfacialregion 308). In particular embodiments of the invention, the processingtreatment performed during step 806 includes a second annealingtreatment.

In particular embodiments of the invention, the second componentprovided in step 808 includes a back-contact layer. In more particularembodiments of the invention, the back-contact layer includes aplurality of layers. In such specific embodiments of the inventionwherein the back-contact layer includes a plurality of layers, theback-contact may be assembled layer-by-layer, that is, sequentially,adjacent the CdTe layer. A non-limiting example of such layer-by-layeror sequential assembly of the back-contact layer includes a procedurewhereby each of the plurality of layers is disposed one after anotheradjacent the CdTe layer. Non-limiting examples of methods via which thesecond component, or components layers thereof, may be disposed adjacentthe CdTe layer include deposition methods including at least one ofscreen printing, sputtering, evaporating, electroplating,electrodepositing, or electroless plating.

Based at least on the methods presented in FIGS. 1-2, and 8, and theexperimental results presented in FIGS. 5-7, it may now be evident ofone of skill in the art that, quite generally, the presence of a p-typedopant during an annealing treatment (for instance, the first annealingtreatment as recited in step 106, or in step 206) can be utilized toobtain enhanced p-type doping levels within a CdTe layer (for instance,the CdTe layer recited in step 102, or in step 202).

FIG. 9 is a flow-chart illustration of a method 900 of p-type dopingCdTe, according to one embodiment of the invention. The method 900includes a step 902 of providing a first component including CdTeincluding an interfacial region. This is to be followed by a step 904 ofsubjecting the CdTe to a functionalizing treatment to obtain p-typedoped CdTe, the functionalizing treatment comprising a thermal treatmentof at least a portion of the interfacial region in the presence of afirst material comprising a p-type dopant, and of a second materialcomprising a halogen. In particular embodiments of the invention, thefunctionalizing treatment recited in step 904 includes depositing thefirst material on at least a portion of the interfacial region prior tothe thermal treatment.

In particular embodiments of the invention a physical form of the CdTeas recited in step 902 is polycrystalline. In particular embodiments ofthe invention, the first material recited in step 904 comprises aliquid, or a gas. In more particular embodiments of the invention, thesecond material recited in step 904 comprises a liquid, or a gas.

Non-limiting examples of the p-type dopant recited in step 904 includebismuth, phosphorous, arsenic, antimony, gold, or copper. Non-limitingexamples of the second material recited in step 904 include cadmiumchloride, hydrochloric acid, chlorine gas, or combinations thereof. Inparticular embodiments of the invention, the first material recited instep 904 further comprises at least one of EDA, a dilute solution ofbromine in methanol, or a mixture of nitric acid and phosphoric acid.

Based on experiments, representative results of which are presented inFIGS. 5-7, in more particular embodiments of the invention, a ratio ofan amount of the first material to an amount of the second material, asrecited in method 900, should lie within the range from about 0.01 ppmto about 100 ppm.

In particular embodiments of the invention the thermal treatment recitedin step 904 includes a first annealing treatment. In particularembodiments of the invention, said first annealing treatment isperformed at temperatures that lie within a range from about 300° C. toabout 500° C. In particular embodiments of the invention, said firstannealing treatment is performed for a time period that lies within arange from about 1 minute to about 60 minutes. In particular embodimentsof the invention, said first annealing treatment recited is performed sothat an environment of the green component during the first annealingtreatment comprises an oxidizing environment.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:

1. A method of p-type doping cadmium telluride (CdTe), said methodcomprising the steps of: (a) providing a first component comprisingcadmium telluride (CdTe) comprising an interfacial region; and (b)subjecting the CdTe to a functionalizing treatment to obtain p-typedoped CdTe, said functionalizing treatment comprising a thermaltreatment of at least a portion of the interfacial region in thepresence of a first material comprising a p-type dopant, and of a secondmaterial comprising a halogen.
 2. The method of claim 1, wherein thep-type dopant comprises bismuth, phosphorous, arsenic, antimony, gold,silver or copper.
 3. The method of claim 1, wherein a ratio of an amountof the first material to an amount of the second material lies withinthe range from about 0.01 ppm to about 100 ppm.
 4. The method of claim1, wherein a physical form of the CdTe is polycrystalline.
 5. The methodof claim 1, wherein the second material comprises cadmium chloride,hydrochloric acid, chlorine gas, or combinations thereof.
 6. The methodof claim 1, wherein a physical form of the first material is selectedfrom the group consisting of liquid, and gas.
 7. The method of claim 1,wherein a physical form of the second material is selected from thegroup consisting of liquid, and gas.
 8. The method of claim 1, whereinthe functionalizing treatment comprises depositing the first material onat least a portion of the interfacial region prior to the thermaltreatment.
 9. The method of claim 1, wherein the first material furthercomprises at least one of ethylene di-amine (EDA), a dilute solution ofbromine in methanol, a mixture of nitric acid and phosphoric acid, andcombinations thereof.
 10. The method of claim 1, wherein the thermaltreatment comprises a first annealing treatment.
 11. The method of claim10, wherein the first annealing treatment is performed at temperaturesthat lie within a range from about 300 degrees Celsius to about 500degrees Celsius.
 12. The method of claim 10, wherein the first annealingtreatment is performed for a time-period that lies within a range fromabout 1 minute to about 60 minutes.
 13. The method of claim 10, whereinan environment of the CdTe during the first annealing treatmentcomprises an oxidizing environment.
 14. The method of claim 1, whereinthe p-type dopant comprises copper phosphorus, arsenic, antimony, gold,silver, bismuth, or combinations thereof.
 15. The method of claim 1,wherein the halogen comprises chlorine.
 16. A method of making aphotovoltaic cell, said method comprising the steps of: (a) providing afirst component comprising a cadmium telluride (CdTe) layer comprisingan interfacial region; (b) subjecting the CdTe layer to afunctionalizing treatment to obtain a green component, saidfunctionalizing treatment comprising a thermal treatment of at least aportion of the interfacial region in the presence of a first materialcomprising a p-type dopant, and of a second material comprising ahalogen, wherein the functionalizing treatment effects an incorporationof the p-type dopant into the CdTe layer; (c) subjecting the greencomponent to a processing treatment; and (d) disposing a secondcomponent adjacent the CdTe layer to form the photovoltaic cell.
 17. Theprocess of claim 16, wherein the thermal treatment comprises a firstannealing treatment.
 18. The method of claim 17, wherein the firstannealing treatment is performed at temperatures that lie within a rangefrom about 300 degrees Celsius to about 500 degrees Celsius.
 19. Themethod of claim 17, wherein the first annealing treatment is performedfor a time-period that lies within a range from about 1 minute to about60 minutes.
 20. The method of claim 17, wherein an environment of theinterfacial region during the thermal treatment comprises an oxidizingenvironment.
 21. The method of claim 16, wherein the functionalizingtreatment comprises depositing the first material on at least a portionof the interfacial region prior to the thermal treatment.
 22. The methodof 16, wherein the processing treatment comprises a soaking treatment.23. The method of claim 22, the solvent treatment comprises the use of asolvent comprising ethylene di-amine.
 24. The method of claim 16,wherein the processing treatment comprises deposition of a copper layeron at least a portion of the interfacial region.
 25. The method of claim16, wherein the processing treatment comprises a second annealingtreatment.
 26. The method of claim 16, wherein the first componentcomprises a layer comprising a transparent conducting oxide.
 27. Themethod of claim 26, wherein the transparent conducting oxide comprisesaluminum doped zinc oxide, indium tin oxide, fluorine tin oxide, cadmiumtin oxide, or combinations thereof.
 28. The method of claim 16, whereinthe first component comprises a layer comprising a high resistanceoxide.
 29. The method of claim 28, wherein the high resistance oxidecomprises zinc tin oxide, aluminum oxide, tin oxide, gallium oxide,silicon oxide, indium oxide, or combinations thereof.
 30. The method ofclaim 16, wherein the first component comprises a layer comprisingcadmium sulphide.
 31. The method of claim 16, wherein the secondcomponent comprises a back-contact layer.
 32. The method of claim 31,wherein the back-contact layer comprises a plurality of layers.
 33. Themethod of claim 32, wherein each of the plurality of layers is disposedsequentially adjacent the CdTe layer.
 34. The method of claim 16,wherein disposing the second component is performed via a depositionmethod comprising at least one of screen printing, sputtering,evaporating, electroplating, electrodepositing, or combinations thereof.35. The method of claim 16, wherein the second material comprisescadmium chloride, hydrochloric acid, chlorine gas, or combinationsthereof.
 36. The method of claim 16, wherein a ratio of an amount of thefirst material to an amount of the second material lies within the rangefrom about 0.01 ppm to about 100 ppm.
 37. The method of claim 16,wherein the p-type dopant comprises copper phosphorus, arsenic,antimony, gold, silver, bismuth, or combinations thereof.
 38. The methodof claim 16, wherein the halogen comprises chlorine.